Transmission system



March 9, 1937. R B. LORD 2,073,451

TRANSMISSION SYSTEM Filed Jan. 2; I935 INVENTOR R. B. LORD A T TORNEVPatented Mar. 9, 1937 TRANSMISSION SYSTEM Reginald B. Lord, Los Angeles,Calif., assignor, by

mesne assignments, tqWestern Electric Gom- T pany Incorporated, acorporation of New York UNITED STATESVPATENT OFFICE Application January2, 1985, Serial N8. 87

In Great Britain June 6, 1934 I 13 Claims.

l1) plying separate signal currents independently to' the respectivedevices and, at the same time, preventing one device from responding tothe signal current intended for the other device.

For convenience of description, the invention 1,; has been embodied in afilm sound recording system. The invention is not thereby limited tofilm sound recording, but' may be embodied in any desired signaltransmission system such as telegraph, telephone, radio, television,telephotog- 2O raphy, telemetering and similar systems.

;In film sound recording systems in which a record of varying density isproduced by a light beam modulated by a pair of shutters or ribbons,,due to the finite height of the recording beam, certain inaccuraciesare produced in the record.

It has recently been proposed to actuate the shutters orribbonsindependently with power from separate channels connected to thesource ofsignals, A phase shifting network is incorporated in onechannel and delays the signal current supplied to one shutter or ribbonwith respect to the signal current supplied to another shutter orribbon. In such a recording system, the direct signal current and thedelayed signal current must be kept separate and each permitted toactuate only one of the shutters or ribbons.

- Recording systems are also known in which the position or spacing ofthe recording device is controlled by a slowly changing unidirectionalbiasing current varying with some function of the signal amplitudes,thus producing a reduction in the film noise produced duringreproduction. The present invention permits the biasing current from anoise reduction control circuit to be applied to a phase shift recordingcircuit in such manner that the unidirectional current from the noisereduction circuit does not changethe electrical constants of the phaseshift channel or the direct signal channel. In the drawing: 7 I Fig. 1is a simplified diagrammatic sketch of the invention; 7 l

Fig. 2 is a simplified diagrammatic sketch of the invention applied totransformer terminated signalchannels; g

Fig. 3 is a modification of Fig. 2; I

Fig. 4shows diagrammatically a phase shift noise reduction soundrecording system embodying the circuit of Fig. 2; I

. Fig. 5 shows a modified system embodying the circuit of Fig. 3. I

In Fig. 1, a signal responsive device 5, and an element 28 having thesame impedance as the device 5.are connected in serial relationshipacross channel. A pair of elements 36, 31, having equal impedancesarevalsoconnected in serial relationship across the terminals 45, 46 ofthe signal transmitting channel. Signal currents will flow through thedevice 5 and the element 20, and, as

the. terminals 45, 46 of a signal transmitting v these are of equalimpedance, they will cause equal potential losses, thus the junction,,l9will havea potential, midway between the potentials of the terminals ofthe signal transmitting channels. Similar1y,.signal currents will flowthrough the elements31 and 36, andas theseelements are of equalimpedance, the wire 38 will be at a potential midway between thepotentials of the terminals of the signal transmitting channels. Thusthe signal currents do not produce any difierence of potential betweenthe junction l9 and thewire 38. The junctionJB and the wire 38 are thusin conjugate relationship with the terminalsAS, 46 of the signaltransmitting channel; 1

Similarly, in Fig. 1, a signalresponsive device 6 and. an element 38having the same impedance as the device 6 are connected in serialrelationship across the terminals 41, 48 of a secondsignal transmittingchanneL- A pair of elements34, 35 having equal impedances are alsoconnected in serial relationship across the terminals 41, 48 of thesecond signal transmitting channel. In this case, the signal currentsfrom the second signal transmitting channel do not produce anydifierenceof potential between the junction l9 and the wire 33. Againthe junction .l9 and wire 33 are in conjugate relationship with the.terminals 41, 48 of the channel.

- As the signal transmitting channels are only joined at the junction19, signal currents from one channel will, not fiow through the device.

which is responsive tdthe sigrialsfrom, the other channel. z p

A control or biasing circuit may be attached to the, wires 33 and 38. Asthe; signal currents do not produce any potential. difference between iCurrent from the control circuit will flow through element 31 and signalresponsive device 5 in series, thus biasing the device 5. Current willalso flow through elements 36 and 20 in serial relationship. But,element 31 and device 5 have the same total impedance as elements 36 and28. The control current thus divides equally in the two paths. Aselements 36 and 31 are of equal impedance and traversed by equalcurrents, the potential drops in the elements are equal. Thus theterminals: 45, 46 of the signal transmitting channel are at equalpotentials with respect to the biasing current, and. no biasing currentwill flow in the signal transmitting channel.

Similarly, the current from the control circuit will flow equally in theelement 30 and. the device 6, thus biasing the device 6. And, aselements 34 and 35 are of equal impedance, the terminals 41, 48 of thesecond signal transmitting channel are at equal potentials and nobiasing current will flow in the second signal transmitting channel.

Due to the balanced condition of the two bridges thus formed eitherjunction of the first bridge may be connected to either junction of thesecond bridge, and the control circuit connected to the remaining twojunctions. Also,

the equal elements may be interchanged in position, for example, thepositions of device 5 and element 20 may be interchanged, and thepositions of device 6 and element 30 may be interchanged.

In Fig. 2, the signal transmitting channels respectively terminate inthe primary windings of the transformers II and 28. The secondarywindings of the transformers l1 and 28 are respectively connected to thesignal transmitting channel terminals. As before explained, current fromthe control or biasing circuit will not flow in the secondary windingsof the transformers I7 and 28, thus preventing the control currents frommagnetizing the cores of transformers l1 and 28.

In Fig. 3, the secondary windings of transformers l1 and 28 areaccurately tapped in the center, and the taps connected to wires .38 and33. In this case, the impedances of the halves of the secondary windingof transformer take the place of the elements 36 and 31 in Fig. 1.Similarly, the impedances of the halves of the secondary winding oftransformer 28 take the place of the elements 34 and 35 in Fig. 1.

In Fig. 4, light from a source I is focused by the lens system 2 on thealigned orifices 3 pierced in the pole-faces of the magnet 4. A .pair ofshutters or ribbons 5, 6 define the height of the beam of lighttransmitted through the orifices 3. An image of the slit thus formed isfocused by the lens 1 on the film 8, traversed in the usual manner fromthe reel 9 to the reel It).

An opaque plate ll, pierced by a suitable orifice, protects the filmfrom undesired light. The shutter 5 is placed vertically above theshutter 6 in a plane parallel to the plane of the film 8. When signalcurrents flow in the shutters or ribbons 5 or 6, the magnetic fieldsproduced by the currents will react with the field of the magnet 4 toproduce an oscillation of the shutters 5 or 6 having a component ofmotion in the direction of the motion of the film 8. If identicalcurrents simultaneously fiow in both the shutters or ribbons 5 and 6,the impressions produced on the film 8 will not coincide in position,due to the finite height of the recording slit defined by the shuttersor ribbons 5 and 6. The record produced is thus not perfect, and a lossof the high frequencies results.

While for convenience a specific form of light valve has been described,the invention is in no way limited to this form of light valve but isapplicable to many other forms. The shutters which control the recordingbeam may be mounted upon stretched ribbons which conduct the signalcurrents, or they may be mounted upon a resilient spider driven by acoil traversed by the signal currents. Or, the shutter may be mountedupon or formed of a stretched magnetic ribbon with the signal currentsimpressed on a coil mounted upon the pole pieces of the magnet.

A microphone I2, with amplifiers l3, l4 forms a source of signalcurrents supplied to the recording bus-bars l5, l6. Any other suitablesource of signal currents may be used and the invention is in no waylimited to the source disclosed.

Signal currents flow from the bus-bars |5, |6 through transformer wire39, to the shutter or ribbon 5, thence through wire l9 and resistor 20to transformer causing the shutter or ribbon 5 to oscillate inaccordance with the signal currents.

Signal currents also flow from the bus-bars I5,

l6 through the phase shift network formed of the series resistor 2|,series inductors 22 and 23, series capacitor 24 and the shunt capacitors25, 26 and 2! through transformer 28, wire 29, to the shutter or ribbon6, thence through wire I9 and. resistor 30 to transformer 28 causing theshutter or ribbon 6 to oscillate in accordance with the currents. Thephase shift network delays the current in this channel with respect tothe current in the channel to the shutter or ribbon 5 for a timeinterval related to the time required for an element of the film 8 topass through the recording light beam.

Current from a suitable source, such as the battery 3|, flows throughwire 33 to the junction of the equal resistors 34, 35. One part of thecurrent fiows through resistors 34, 3|], 20, 36 wire 38, and resistor 32to battery 3|. Another part flows through resistor 35, wire 29, shuttersor ribbons 6 and 5, wire 33, resistor 31, wire 38, resistor 2 to battery3|. If resistor 34 is equal in resistance to resistor 35, no currentwill flow in the secondary winding of transformer 28, thus preventingthe core of transformer 28 from becoming magnetized and changing theelectrical constants of the phase shift channel. Similarly, theresistors 36 and 31 prevent the core of transformer H from becomingmagnetized. Also, if the resistances of the resistors 20 and 33 arerespectively equal to the resistances of the shutters or ribbons 5 and6, no current from the battery 3| will flow in the wire IS. The currentfiowing in the shutters or ribbons 5 and 6 will draw the shutters orribbons 5 and 6 nearer together, thus reducing the film noise in theknown manner.

Signal currents from the bus-bars |5, |6, suitably amplified in theamplifier 40, is transmitted through transformer 4| to the full waverectifier 42 and charge the capacitor 43. The charge on the capacitor 43leaks through the resistance 44' and decreases the efiect of the currentfrom the battery 3| on the recording device, permitting the spacing ofthe shutters or ribbons 5 and 6 to increase as the amplitude of thesignals increases.

In Fig. 5, the secondary windings oi the transformers "H and 2 8areac'curately tapped at the "center-point. Inf this case, the current fromwire 33 fiows equally through the two halves of the secondary winding oftransformer 2 8, but in opposite directions soth'at' the magneticeffects of the two currents balance each other and no magnetization ofthe core of the transformer is produced; "Similarly, the current-towiref38 flows equally, through the two halves of the secondary windingcftransformer l1 and no magnetization of the core is produced. In thiscase, the resistances 34, 35, 36, 31 are not necessary and may beomitted.

What is claimed is:

1. In combination, a recording channel, a recording device and anelement of equal impedance connected in serial relationship to theterminals of said channel, a pair of equal impedance elements alsoconnected in serial relationship to the terminals of said channel, thejunction of said device and said first element and the junction of saidequal impedances being in conjugate relationship with the terminals ofsaid channel, a second recording channel, a second recording device anda second element of equal impedence connected in serial relationship tothe terminals of said second channel, a second pair of equal impedanceelements also connected in serial relationship to the terminals of saidsecond channel, the junction of said second device and said secondelement and the junction of said second pair of elements being inconjugate relationship with the terminals of said second channel, onejunction associated with said first channel being connected to ajunction associated with said second channel, and a control circuitconnected to the other junctions.

2. The combination in claim 1 in which sai recording devices areincorporated in one unitary structure.

3. The combination in claim 1 in which said recording channels carrycurrents from a common source, one channel comprising a phase shiftingnetwork.

4. The combination in claim 1 in which said control circuit supplies aunidirectional current varying with some function of the currentsrecorded.

5. The combination in claim 1 in which said recording devices arestretched conducting ribbons immersed in a common magnetic field.

6. In combination, a recording channel, a transformer having its primarywinding connected to said channel, a pair of equal impedance elementsforming a secondary winding of said transformer, a recording device andan element of equal impedance connected in serial relationship to theterminals of said secondary winding, the junction of said device andsaid element and the junction of said equal elements being in conjugaterelationship to the secondary terminals of said transformer, a secondrecording channel, a second recording device and a second element ofequal impedance connected in serial relationship to the terminals ofsaid second channel, a second pair of equal impedance elements alsoconnected in serial relationship to the terminals of said secondchannel, the junction of said second device and said second element andthe junction of said second pair of elements being in conjugaterelationship to the terminals of said second channel, one junctionassociated with said first 75 channel being connected to one junctionassociated withsaid second channel and a control -arena-teammatetheother ut-1mm;-

7,: The combination in claim 6 in -which said recording ev ces-arincorporated in" one em r I g, gm a' cornmon -magnetic field.

The combination in claim 6 in which said recording currents from "acommon source'onechannel comprising'a phase shifting network.

10. The combination in claim 6 in which said control circuit supplies aunidirectional current varying with some function of the currentsrecorded.

11. In a transmission system, in combination, a signal transmittingchannel, a signal responsive device and an element of equal impedanceconnected in serial relationship to the terminals of said channel, apair of equal impedance elements also connected in serial relationshipto the terminals of said channel, the junction of said device and saidfirst element and the junction of said equal elements forming the freeterminals of a balanced bridge, a second signal transmitting channel, asecond signal responsive device and a second element of equal impedanceconnected in serial relationship to the terminals of said channel, apair of equal impedance elements also connected in serial relationshipto the terminals of said channeLthe junction of said second device andsaid second element and the junction of said second pair of equalimpedances forming the free terminals of a second balanced bridge, onefree terminal of said first bridge being connected to a free terminal ofsaid second bridge, and a control channel connected to the other freeterminals of both bridges.

12. In a transmission system, in combination, a signal transmittingchannel, a transformer having its primary winding connected to saidchannel, a pair of equal impedance elements forming a secondary windingof said transformer, a signal responsive device and an element of equalimpedance connected in serial relationship to the terminals of saidsecondary winding, the junction of said device and said element and thejunction of said equal elements being in conjugate relationship with theterminals of said secondary winding, a second signal transmittingchannel, a second signal responsive device and a second element of equalimpedance connected in serial relationship to the terminals of saidchannel,.a pair of equal impedance elements also connected in serialrelationship to the terminals of said channel, the junction of saidsecond device and saidsecond element and the junction of said equalimpedances being in conjugate relationship with the terminals of saidsecond channel, onejunction of said first channel being connected to onejunction of said second channel, and a control channel connected to theother junctions.

13.In a transmission system, in combination, a signal transmittingchannel, a transformer having its primary winding connected to saidchannel, a pair of equal impedance elements forming a secondary windingof said transformer, a signal responsive device and an element of equalimpedance connected in serial relationship to the terminals of saidsecondary winding, the junction of-said device and said element and the'mbina ion' clai'rn 6 in which said reref-stretched conducting ribbons10 serial relationship to the terminals of the secondary winding of saidsecond transformer, the junction of said second device and said secondelement, and the junction of said second pair of elements being inconjugate relationship with the terminals of the secondary winding ofsaid second transformer, one junction of said first channel beingconnected to one junction of said second channel and a control channelconnected to the other junctions.

REGINALD B. LORD.

